Mono- and di-functional polymers (i.e., telechelic polymers that contain two functional groups per molecule at the termini of the polymer) have found wide utility in many applications. For instance, telechelic polymers have been employed as rocket fuel binders, in coatings and sealants and in adhesives. In addition, polymers that contain two hydroxyl groups per molecule can be co-polymerized with appropriate materials to form polyesters, polycarbonates, and polyamides (see U.S. Pat. No. 4,994,526).
A variety of polymerization techniques, such as cationic and free radical polymerizations, have been employed to prepare functional polymers. However, functionality can be best controlled with anionic polymerization. Living anionic polymerization of styrene and diene monomers were first described by Szwarc and his coworkers. See M. Szwarc, Nature 178, 1169 (1956) and M. Szwarc, et al., J.Am.Chem.Soc. 78, 2656 (1956).
Various publications have discussed the use of protected functional initiators to provide telechelic polymers. An early approach to the preparation of telechelic polymers is discussed in D.N. Schulz, et al., J.Polym.Sci., Polym.Chem.Ed. 12, 153 (1974), which describes the reaction of a protected hydroxy initiator with butadiene. The resultant living anion was quenched with ethylene oxide to afford mono-protected di-hydroxy polybutadiene. While excellent functionality (f=1.87-2.02) was achieved by this process, the protected initiator was insoluble in hydrocarbon solution. Therefore, the reaction was conducted in diethyl ether, and as a result, relatively high 1,2 microstructure (31-54%) was obtained.
U.S. Pat. Nos. 5,331,058 and 5,362,699 to Shepherd, et al. discuss the preparation of telechelic polymers in hydrocarbon solutions using monofunctional silyl ether initiators. These monofunctional silyl ether initiators can be useful in producing dihydroxy (telechelic) polybutadienes having desirable characteristics, such as a molecular weight of typically 1,000 to 10,000, a 1,4 microstructure content of typically 90%, and the like.
These and other anionic polymerization techniques, and in particular those using protected functional initiators, can be useful for the preparation of protected functional polymers. However, problems have been encountered in deprotecting or removing the protecting group from functional polymer moieties. Typically, prior deprotecting processes can require the use of costly reagents, result in partial or essentially no cleavage of the protecting group, lack economic feasibility in commercial production (for example, require high temperatures, long reaction times, etc.), alter the polymer structure, and the like.
For example, U.S. Pat. Nos. 5,331,058 and 5,362,699 discuss the use of tetraalkylammonium fluorides in polar solvents as useful desilylation reagents. However, tetraalkylammonium fluoride reagents can be costly and difficult to handle due to their toxicity (see discussion in U.S. Pat. No. 5,376,745). Further, it can be difficult to effectively remove the silyl protecting groups of these types of initiators using tetraalkylammonium fluoride, and other, reagents. Other reagents, such as tert-butyldimethylsilyl triflate, can alter the polymer structure.